It is known to use practise bombs for, training airforce personnel for actual bombing runs. It is also known to use the practise bombs for practising bombing runs. Originally practise bombing was done with live bombs. However besides being unduly expensive this method of practising is also inherently more dangerous than using dummy bombs. Therefore most of the practise bombing is now done with dummy or practise bombs.
It is no longer necessary for the dummy bombs to have the same weight as the real bombs. Pertinent data such as the trajectory and weight of the bomb is entered into the bomb sight computer; and therefore the pilot's actions are the same whatever the weight. The information is in the computer and the bomb release is guided according to the information in the computer Thus it is only necessary that the computer know the correlation between actual bombs and practise bombs.
Until very recently the practise bombs were made of steel. Thus although less expensive than real bombs, they were still relatively expensive and even of greater concern than the expense was the weight of the bombs which made handling and transportation difficult and costly. More recently practise bombs have been fabricated from such materials as fibre glass and/or composites including plastic and metals in combination. These bombs too are relatively expensive and heavy although less expensive and heavy than the steel bombs.
The more expensive the practise bomb the less apt airforces are to use the bombs in practice. The heavier the bomb the harder it is to handle, the more likelihood there is for accidents during the handling of the bombs, and the more expensive it is to ship from the place of manufacture to the site where the bomb is attached to the airplane.
Practise bombs usually have hollow bodies and are shipped empty to reduce the cost of shipping. They are filled with water when attached to the airplanes to add weight. These practise bombs take tremendous stresses and strains during the flight and during the release. In the flights some of the stresses that are placed on the practise bomb occur because of the high accelerations both at take-off and on manoeuvres such as tight turns, dives and climbs during the flight. In addition, during release a high impact device hits the bomb to force it away from the wing. This is necessary because otherwise the bomb immediately of launching has a tendency to rise and strike the wing causing damage to the airplane if not actually destroying the airplane. Therefore a piston hits the bomb as it is released with a high impact forcing it away from the airplane.
It is because of the high stresses and impacts that high grade material has been used in the prior art dummy bombs. Thus, those skilled in the art in the past have used high grade heavy and costly materials for fabricating the dummy or practise bombs instead of less costly material.